a Forest plots for the effects of carrying predicted pathogenic (PP) heteroplasmies on ASD-related neurodevelopmental traits among probands (n = 1938 for all traits). Beta refers to the standardized coefficient, and negative values indicate worse functions. The standard deviation (SD) of each trait is indicated in parentheses. b Bar plots for the family-adjusted prevalence of PP heteroplasmies among probands and siblings. Probands were grouped according to the severity level computed using the equation: (NV-IQ < 70) + (V-IQ < 70) + (VABS in the bottom 25%) + (- ADOS-CS in the bottom 25%). c Forest plots for the odds ratios (ORs) of carrying PP heteroplasmies for improvements in ASD-related symptoms among probands (from top to bottom, n = 1502, 1512, 1510, 1512, and 1516). d Forest plots for the favorable effects of per standard deviation increase in the mtDNA content z-score (mtCNz) among probands without PP heteroplasmies (from top to bottom, n = 1383, 1391, 1389, 1390, and 1395) and among probands with PP heteroplasmies (from top to bottom, n = 119, 121, 121, 122, and 121). Horizontal black lines represent the 95% confidence interval of the effect sizes. Error bars in b represent bootstrapped SEM. Values on the x axes in c and d are shown on a logarithmic scale. NV-IQ: non-verbal IQ; V-IQ: verbal IQ; VABS: the individual’s Adaptive Behavior Composite from Vineland Adaptive Behavior Scales (2nd edition); ADOS-CS: the communication and social total from the Autism Diagnostic Observation Schedule (ADOS); ADOS-RB: the restricted and repetitive behavior total (module 1–3) or the stereotyped behaviors and restricted interests total (module 4) from the ADOS. Because the ADOS records scores of abnormalities, the additive inverse of the original value was used.